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1. Introduction
High levels of psychological stress are linked to poor mental and physical health outcomes [1]. It has been suggested that 75-90% of visits to general practitioners in the U.S. are related to stress, with direct and indirect costs totalling hundreds of billions of dollars annually [2]. Therefore, it is essential to explore approaches that may prevent and/or manage stress in the population.
A growing body of research has linked sedentary behaviour (i.e., sitting or reclining behaviours that expend minimal energy such as television (TV) viewing, sitting at the computer) with poor mental health, and in particular with anxiety [3] and depressive symptoms [4]. Given the possible adverse effect of sedentary behaviour on those mental health outcomes, one could expect sedentary behaviour to also increase level of stress. This is particularly suggested since activities that may theoretically induce stress, such as working on a computer or using electronic devices for purposes including reading the news or engaging with social media, are often undertaken whilst sitting. However, very little research has examined associations between sedentary behaviour and stress, and the limited existing evidence has been inconsistent. For example, in studies that have utilised subjective measures of stress, one prospective study showed that perceived stress was associated with medium levels of television viewing (14-21 h per week) but not overall sitting time, amongst women living in socioeconomically disadvantaged neighbourhoods [5]. In cross-sectional studies, feeling somewhat stressed was associated with higher sitting time in one study of young women [6], while in another study time spent sitting for transport was linked to higher perceived stress in men and women, yet sitting at the computer, watching TV, and work-related and leisure-sitting were not [7]. It is possible that these mixed findings may partly reflect the use of subjective measures of stress which may be subject to social desirability bias, whereby participants are likely to under-report stress or other indicators of adverse mental states [8]. Using objectively-measured indicators of stress might therefore help to minimise some forms of measurement error inherent within subjective tools.
To date, few studies have examined the association between sedentary behaviour and objectively-measured indicators of stress (i.e., using salivary, plasma, urinary, or hair cortisol). Cross-sectional research has shown that TV viewing was associated with lower...